Three related processes are utilized in the electrolytic purification of copper. The processes include electrowinning, electrorefining and copper sheet production. Each process requires a unique combination of reagents to produce a high purity product at the highest possible efficiency. Electrowinning involves the direct electrodeposition of copper from an aqueous copper electrolyte to create a finished product. Electrorefining involves the purification of copper by dissolving an anode into solution and electrodepositing the dissolved copper as a high grade slab onto copper sheet or titanium mandrel. Copper sheet production involves a process of plating copper into thin sheets for use as starter sheets in a solution similar to electrorefining solutions. Copper sheet production is usually electrodeposited at a faster rate than that of electrorefining. Titanium mandrels may be stripped once a day, and to compensate for this electrolyte used for copper sheet production utilizes different reagent levels than that used for electrorefining.
Relatively small amounts of organic compounds such as glue, chloride, thiourea and Tembind.TM. (a lignosulfonate produced by Temfibre Inc. of Temiscaming, Quebec) are added to these electrochemical systems. Both excess supply and insufficient supply of these addition agents result in loss of current efficiency and copper deposit quality. Historically, it has been extremely difficult to control supply of these low level addition agents. The accepted practice has been to simply supply addition agents at constant rates which have been found to produce acceptable results through trial and error. However, in actual commercial electro-processing of copper the electrolyte composition and plating rates are often changing. For example, concentration of copper in the electrolyte and copper deposition rates frequently change. These changing conditions tend to adversely affect the quality of the copper deposited. Without any warning of the effect upon addition agent levels in the electrolyte, adjustments to the addition agents were not made until after production quality had suffered.
There are several possible electrochemical techniques for analyzing addition agent levels. The proposed techniques include potentiostatic transients, chronopotentiometry, cyclic galvanometry, differential pulse polarography, impedance measurements, stripping voltammetry and cyclic voltammetry. These electrochemical techniques have been successfully applied to lead, copper (using a thiourea addition agent) and zinc systems.
Cyclic voltammetry has been successfully used to measure additive levels of glue and antimony in zinc electrolyte (O'Keefe Canadian Patent 1,064,852). In the zinc electrolyte, glue and antimony levels were measured by measuring shifts in recorded portions of a cycle between cathodic deposition of zinc and anodic dissolution of the deposited zinc. However, in actual zinc electrolyte, both glue and antimony reagents are present. The zinc electrolyte process is controlled by trying to keep a pseudoequilibrium cyclic voltammogram plot at or near an ideal condition.
Additionally, in O'Keefe's Canadian Patent 1,064,852, control of a synthetic copper sulfate solution electrolyte having thiourea, chloride and glue reagents, was tested. The electrolyte was also tested in pseudoequilibrium conditions and revealed that thiourea increased the polarization and caused a current peak at about +0.190 V. The method of O'Keefe does not teach testing of glue with Tembind rather than thiourea. To date, O'Keefe's cyclic voltammetry has not been successfully applied commercially in the copper electro-processing industry.
Recently, ASARCO (U.S. Pat. No. 4,474,649) has developed a differential pulse polargraphy technique for testing thiourea concentration in electrolyte used in copper electrorefining operations. This technique has become commercially acceptable for testing thiourea levels in the portion of the copper electrorefining industry using thiourea. However, to date, the differential pulse polarography method has not been adaptable to measure glue with Tembind.
Accordingly, it is an object of this invention to provide a process of effectively monitoring glue with Tembind in complex copper electrolytic solutions.
It is another object of the invention to provide a method of maintaining copper electrodeposition at levels of maximum quality and peak efficiency.
It is still another object of the invention to accurately measure glue concentrations on the order of a few parts per million in copper electrowinning solutions.